With a little luck the aliens would have abandoned Earth, but to our trios dismay, a mothership crashes and aliens survive. Eventually they have no choice but to deal with the aliens as they began to recover and build a city while dismantling their mothership. The alien toil night and day, and soon hatch their offspring, increasing their numbers and seemingly begin to transform Earth back to a humid, highly oxygenated subtropical environment suitable to their liking.
Not all is as it should be. The alien plant genetically alters anything that eats it, and although few organisms survived, those that do quickly get a foothold, and Earth is soon crawling with unimaginable creatures, many that are highly intelligent. It is a new battleground for survival.